The time-dependent electron neutrino survival probability will have a significant impact on the neutrino spectra of the different nuclear reactions. Accordingly, figures REF  and REF  show the spectra correspond to two neutrino types: \(pp\)  and \(^8B\)  neutrinos. An essential difference between these two spectra relates to the thickness of the \(\epsilon _\phi \)  band for a fixed value since thickness decreases with neutrino energy. Therefore the \(\epsilon _\phi \)  band is more significant for a \(pp\)  spectrum than for a \(^8B\)  neutrino spectrum. This is an effect identical to the one discussed previously for the \(P_{ee}(E,\phi ) \)  functions. Therefore, the measurement of solar neutrino fluxes and solar neutrino spectrum in the energy range below \(0.2\; MeV\)  will provide the strongest constraint for such a class of dark matter models. Figure REF  and REF  show the spectra of \(^8\) B and \(pp\) , if we assume the precision expected to be attained by the Darwin experiment [1]}.
Figure REF  also shows the precision expected for the Darwin experiment.
